Is expiation obligatory upon one who intended an oath in his heart (without uttering it) and then broke this commitment?

If an oath is not uttered, then there is nothing binding upon a person, according to the Prophet’s (peace be upon him) saying: “Indeed, Allah has pardoned for my Ummah what they whisper to themselves, as long as they do not speak of it or act upon it.” Uttering the oath is a pillar for its validity.